In the reception and handling of 911 emergency telephone calls, it is important to be able to automatically pinpoint the location of a caller; e.g. an anxious or hysterical caller unable to tell his or her location, or a caller that does not know his/her location and has no visible landmarks that could be used to fully identify such. In calls over ordinary telephone sets directly linked by wire to the Public Switched Telephone Network (hereafter, PSTN), it is possible to trace the number of the telephone from which the call is placed and use that information to locate the caller, since the calling device or unit is associated with a known “building” address from which the caller's location is easily implied or determinable.
However, such fixed or predefined location is not available when the respective calling unit is mobile; e.g. a cellular telephone, “2-way” pager” or other wireless device. Mobile units of this kind generally link to the PSTN through a network of geographically dispersed antennas, base stations and switching offices. Although such units have an identity which is signaled during a call, that identity neither implies their physical location nor forms a basis for calculating it. Furthermore, even if the locations of the antennas and distances between them are known, that information per se does not form a basis for determining the location of a unit with which they are currently communicating. Such fixed or predefined location might not be available if the call/request is made through a network where such “building” address is not documented (i.e. IP based networks).
The federal communications commission (FCC) has specific requirements for wireless 911 calls. These requirements are divided into two parts—Phase I and Phase II. Phase I requires carriers, upon valid request by a local public safety answering point (PSAP), to report the telephone number of a wireless 911 caller and the location of the cell sector that received the call.
Phase II requires wireless carriers to provide far more precise location information. For carriers that have implemented a handset solution, the FCC requirement is that 67% of the calls are accurate to within 50 meters, and 95 percent of the calls are accurate to within 150 meters. For a network-based solution, the requirement is that 67% of the calls are accurate to within 100 meters, and 95 percent of the calls are accurate to within 300 meters. In response to such regulatory requirements, there is a need to provide a method and system for providing 911 services in a wireless communication system.
Future networks and technologies are anticipated to support location based services beyond E911 calls. Such applications might include location-based advertising, location of relatives, integrated mapping services etc. Therefore, there is a need for networks that can support accurate location of the user.
In code division multiple access (CDMA) networks, all sites are synchronized so the code sequences begin at the same time. When a fiber fed distributed antenna system (DAS) network is introduced to a CDMA network, the fiber delay impacts the synchronization for that network. With any DAS network that has simulcast nodes, care must be taken to ensure the fiber delays and differential fiber delays between the nodes are taken into account. The following three CDMA parameters must be used to ensure the delays are accounted for:                Tx Delay—the propagation delay on the transmission (Tx) path between the CE (Channel Element) and the first node of the simulcast sector        Rx Delay—the propagation delay on the reception (Rx) path between the CE and the first node of the simulcast sector        Max Differential Delay—this is the delay difference between the first and the last node of the simulcast sector        
These parameters normalize the delays of the fiber transport to allow the data to fall into synchronized search windows for the mobiles serving in the simulcast coverage area. Without utilizing these parameters, the Tx and Rx data transmitted by the simulcast sector will fall outside the search window.
Although accounting for the fiber delays on the simulcast sector using the parameters works for communicating with mobiles in the simulcast serving area, there is still an inherent accuracy problem for location base services and E911. Whenever the location calculation reverts to triangulation in order to determine a mobile's location, it requires a reference latitude/longitude and calculates the mobiles distance based on timing and the reference latitude/longitude. With a DAS simulcast sector, this reference latitude/longitude can be miles from the actual mobile location, yet the calculation of the RF delay for triangulation purposes will show the distance of the mobile to be at a closer distance due to its proximity to a nearby simulcasting node and not the actual reference location. Therefore, there is a need for a system that normalizes all simulcasting nodes.